Picture-transmission system



June 19129. H, E, w55 1,717,781

l PI'HIR? TRANSMISSION SYSTEM v mea umn ze, 192s x j /ao una' VALVE byAf/y sary to secure proper tone reproduction, as

is subsequently/explained.

Patentes June 1s, 1929.

uNiTsD sra'ryas Arizrrlr orrca.

aannam' a meer MoN'rcL LABORATORIES, YORK.

l Hernan-TRANSMISSION l YsTEM'.

AIR, NEW JERSEY, INCORPORATED, OF NEW YORIL -N. Y., a conronATroN or NEWApplication led March 2G, 1926. Serial No. 97,659.

c This invention relates to picture transmisdsion systems.

An object of this invention is to control the tone-characteristic of thereceived picture in such a manner that the in a single photographicpensated Ofor and thereby operation is eliminated.

A feature of this invention apertured diaphragm dr screen light wedgescreen placed 1n the distortion inherent operation is comonephotographic is a yspecial or a special optical portion of the system atthe receiving end.

A' further feature is the employment of an optical system in whic lightvalve are removed by optical means to l the vfirtual light valve. 20

a point in space outside the proper, thus producing a virtualpositioning of the special screen at The special screen at the lightvalve,

and the may howeverbe placed h the jaws of the light valve light valve,

though when so positioned it is not asaccessible and must beconsiderably smaller. v

The electrical picture transmission systems now in general operationhave a linear characteristic and a strictly r 1s maintained betweenectilinear relation the light-incident at the sending end and the lightreceived from the apparatus at the receiving end. The pictures to betransmitted ing apparatus'usually tive transparency and to in order tosecure are placed on the sendin the form of a posiare received as anegative from which photographic positive prints are made in turn. Thisprocedure is adhered correct tone rendering as two photographicoperations awre neces- The photographic proc general in a mental mannerandit is, necessary in photography photographic operations,

* and positive, lto reproduce v mission. Thusif'the ihn the originalobject. Itmatching of the character tive and the positive thareproduction is obtai ess reproduces ein' reciprocal instead of acompletherefore always togo through two namely, negative the tone valuesof'A is` by the properistics of the negat a correct linear ned and .itfis .required that the' photographic operations be performedalways inpairs. This-characteristicl of the photographic process puts certainlimitations upon'the'lexibility of picture transis a positive, anegative from` which .prints must 1nat the sending'end must be received,

turn be made; and

on a curved acterlstlc.

valve. being madethereby easily accessible;

if a negative lis used in send' g, a positive is received. Thelimitations just tothe method of reproduction, in which the picture isbuilt up of lines of variable density.

ere lines or other elements of but of constant density are used,positives may be received from positivesby reversing the photoelectriccell connections. tives, however, cannot be received from negatives for,although they look like the originals when viewed under conditions suchthat the structure is invisible, they will not print in the same manner.

In order to shortenA the overall time in picture transmission'and forother-obvious reasons it desirable to eliminate one photographicoperation, and this may be accomplished b tions of the photographicprocess which require two operations for correct tone rendering. Oneessential step is to have the sending apparatus so connected that thetwo ends of the tone scale are rendered' as of the values of those atthe sending` end, namely,.hlacks must benrendered as blacks andwhites-must hev rendered as whites. Since ,the photo- Nega- ASSIGNORJTOBELL TELEPHONE graphicip'rocess reproduces in general in a reciprocalmanner, as already pointed put, the problem becomes one. of s o warpingthe characteristicsof the picture transmissipn system between these endpoints that the nonlinear characteristic inherent in the photographicprocess when carried `through only i one of the two operations iscompensated for. One method of doing this is to warp the electricalcharacteristics, which can be dond-by setting the'tw'o picture endpoints portion of the modulator char- ,Similar troduced elsewhere. Themethod which is this invention consists of ,distorting the illuminationcurrentrelation of distortionmight be inthe light valve by diaphragms orscreens or light absorbing wedges over the light valve opening..thereby' causing loptical' distortion. The application of-this method isfacilitated by the adoption 'of an optical systemlin which valve are?removed by valve proper,

and at vthe same time ofconsiderably larger size than'wlien locatedinside the valve.

'Ihe method of introducing optical distorleo I' sultant photograph overtion disclosed herein comprises lacing diaphragms or screens or lightabsor ing wedges over the aperture of the light valve or preferably overthe virtual light valve opening on the projection lens nearest the ilinto provide a graded light transmission by exposing varying lengths ofaperture or varying light be-th'e case and thus produces acharacteristic in which the exposure increases .more'rapidly than thecurrent through the light valve ribs bon. The exact forinof the aperturein the diaphragm or screen must be such that when the lightvalve'current and the receiving end lamp are adj ustedto ive white andblack on the exposed film fo opacity, respectively, at the sending end,the

'intermediate tones will be exact copies of those of the sending. film.It will then be possible to reproduce a negative as a correct printingnegative and a positive as a positive ready for viewing or copying.

Some of the geieral features of the invention have been broadly outlinedabove. Further objects and features will appear and a betterunderstanding of typical embodiments will be had fromthe followingdetailed de- -.scription in connection with the accompanying drawings.

' valve.A

strictly linear 'mitted' so that the AReferring to the drawings:

Fig. l is a set of curves showing characteristics 'of photographicaction.

. Fig. 2 is a Adiagrammatic representation of -an optical systememployed at the receiving station in a picture transmission system.

zFigc shows the light valve opening and ribbon image thereon.

v Fig. 4 shows types of apertures applicable to a special screens ordirect current light Figi Fig. 6 shows `a special light wedge screenapplicable to a direct current light valve.-

A picture transmissionsystem, in order to receive a facsimilereproduction, must be so set up that the current delivered to the lightvalve increases Vith decreasing illumination of the photoeleictic celland vice-versa, and when `so set up the ictures may be translacks arereceived `as blacks and the whites as whites. However, in the' usualtransmissibn system having a characteristic, the intermeiiiediate tonesare badly distorted. This is shown diagrammatically in Fig. lwhere the Asuitable diaphragm'or screen may the film less than would normallysignificance for clear film and entire- 5 yshows types of specialscreens or apertures applicable to an alternating current light valve.

tated by v alve, l horizontally, 15 is a lens which forms' an en-lillumination of the photoelectric cell which corresponds to thebrightness of the original object is given by the 'abscissae I and thetransmitting or reiiecting, power of the photo? graphic impressionobtained is shown by the ordinate t.- Curve A shows the transmission,

with the ordinary arrangement of the apparatus, ofthe developed hlm atthe receiving end, and curve B shows the transmission of the receivedfilm when the polarity' of the pliotoelectric cell is'reversed; thedaiks for the curve B are the reverse of those for the curve A. It willbe seen that in curve B the relationship between exposure andtransmission is a steeply descending curve instead of the straight lineC which is required The lights and for truthful reproduction. L`It maybe pointed out that photographic characteristics are usually plotted iiithe logarithmic form proposed by I-Iurter andvDriflield, and when soplotted appear,I as straight lines. This method of plotting tends toobscure the present purpose, that the actual relation, for a singlephotographic operation, is represented, on a linear scale, as apronounced curve, as shown Fig. 1. The result of xthis is that there israpid increasein density in the tones very/'near white, and that thedark tones are all practically indistinguishable. The characteristic as'sh wn in either curve A or B varies with `the exposure and developmentbut always has the general form shown.A In ordinary photography themedium on which a print is made has a similar characteristic, so thatbymatching or opposing two characteristic curves, truthful reproduction isattained upon the completion of the two operations of negative andAprint making. In order, for the purpose of single operation picturetransmission, to correct the characteristic from the form shown in curvethe fact, which is of 4 B into a correct linear characteristic as shownby the straight line C, it is necessary to introduction of specialdiaphragms or screens covering the light valve aperture.v As alreadypointed out the practicability of using special apertures in this way isgreatly facilithe use of anoptical system in which light valvehave beenremoved the jaws of the from the vimmediate proximity of the light valveribbon to a point in space where an enlarged image of theribbon isformed.

An optical system, adapted to the reception of pictures in accordancewith this system is diagrammatically shown herein in Fig. 2. In thisfigure 10 is the light source, 11 is a condensing lens, 12, is the bodyof the light valve,

14 is the light valve-ribbon, which lies 13- is the opening through thelight I larged image `of the ribbon on the special aperture 16-positioned as nearly as practi. cable in the image plane of the lensand in front of the lens 17 which in turn forms an' image of therectangular aperture 18 on the film 19. lTypes, of screens which may beused at 16 are shown in Figs. 4, 5' and 6.

' With this optical system an image of the aperture 18 of fixed andconstant size falls on the film with a brightness whichdepends upon theexposure through the apertures 16.

This in turn is determined by the size of the image of the ribbonwhichfalls across it. By

proper adjustment, the ribbon image may be made to just cover theaperture 16 whenrthe ribbon is stationary so that the edges of theaperture become virtually the Alight Valve jaws of the usual rectangularlight valve construction. In this arrangement. diaphragms or screens ofvarious shapes or distributors of density forming the aperture 16 alterthe amount of light falling on the ilm'for-the various positions oftheribbon image, but do not alter the shape of the image formed by theaperture '18 and focused on the film".

The light valve opening and the action of the ribbon is illustrated inFig. 3. In the optical system here shown, as previously stated, the jawsof the light valve are removed from the immediate proximity ofthe lightvalve ribbon to a point in space where an enlarged image of the ribbonis formed and it is at `this point that the special diaphragm or screenis positioned. The ordinary screen of opaque material 16B having arectangular aperture QOR is shown in Fig. 3 at the left. The middleligure shows the screen 16B with a rectangular aperture and the image14S of the light valve ribbon across it in a position partially openingthe valve as shown by the opened area 21R. Iith the ordinary type ofvalve having a rectangular aperture the opening is obviouslyproportional to the displacement of the ribbon dr its image. At

the right in Fig. 3 is shown a special diaphragm or screen 16A having anaperture 20A so shaped that the amount of light lallowed to passincreases rapidly up tothe point of maximum exposure, the exposed areaof the aperture being such that it is in general proportional to thereciprocal of the displacement of the light valve ribbon. The amount ofdisplacement of the ribbon or its .image 14S is the same as shown in themiddle drawing but the actual opening 21A is much smaller than therectangular aperture 21R or its outline as indicated at 21R on 16A.

Fig. 4 shows a number of typical diaphragms or screens applicable toadirect. current light valve and Fig. 5 those for an alternating currentvalve. Fig. 6 shows a special light wedge applicable to a direct currentvalve. In the direct cur- `rent valve the ribbon has an amplitude ofvibration from one edge of the aperture to the other, while i'n thealternating current valve the ri-bbon has'a'n amplitude of vibrationsymmetrical with the center line of the aperture, one-half thetotalwidth of the aperture on each side. VIn each of these figures-theVshaded portion, designated by 14S, represents the image of the lightvalve y in the position of maximum opening. The dot and dash lines showthe image of the light valve ribbon in its extreme position in the otherdirection. In Fig. 4, 16D shows 4a screen having a symmetrical aperture20D, 16E shows a modified aperture 20E, and 16F shows a furthermodification comprising a plurality of apertures 20F which have theappearance of sawteeth. In Fig. 5, 16A

shows a screen having a symmetrical aperture 20A, 16B shows a modifiedaperture 20B, and 16C shows a plurality of apertures 20C which have theappearance of a double set of saw teeth. In Fig. 6, 16G shows a screenhaving a light wedge aperture or area 20G of varying transparency orlight 'transmitting power. This type of screen while I shown for adirect current light valvemay be readily adapted to an alternatingcurrentY valve. In all cases the various `kinds ofl screens aredesigned. to pass lincreasing; or decreasing increments of light perunit ot movement of the light valvev ribbon andv thus by optical meanssubstantially compensate for distortion in the photographic proc'- ess.The general characteristics 'of the screens aresuch that the passage oflight is approximately proportional to the reciprolgal of thedisplacement of the light valve ribphotographic characteristic. as shownby the. curves in Fig. 1, varies with the exposure and development, itis necessary to adopt a definite iilm emulsion, exposure, anddevelopment, and fit the special screen to these In View the fact thatthe shape of the t conditions. A fairlyy fast emulsion of considerablelatitude such as commercial ortho film is satisfactory. For such a film,diaphragms or screens having apertures lof substantially the shapesshown in Figs. 4 and 5 or equivalent light. wedge screens as shown inFig. 6 provide the necessary correction to produce facsimilereproduction.

With the present form of alternating `cur 'i actuated by current`Which'has been put through an appropriate filtering system so that theentire opening of the light valve is uniformly illuminated.

This invention provides for substantially compensating 'the distortionsin the photographic process, inherent in a single photographicoperation, by means of a special screen over the light valvetherebymaking possible the reception of facsimile reproduction. Thedistortionsit corrects must not be confused with those caused byunskilled manipulation in ordinary photography,such as .under Vor overexposure, or Incorrect development. The electrical picture transmissionsystem offers possibilities of photographic 'prmtingoperations in whichthe ordinary general reciprocal relation between negative and positivedoes not hold and this invention makes use of certain of thesepossibilities.

The invention disclosed is obviously susceptible to modifications andadaptations Without departing from the spirit and scope of the inventionand it is not intended to limit j the invention to the specificconstruction shown and described except as defined. by the scope of theappended claims.

What is claimed'is: 1. -In a picture transmission system,`a receivingdevice including a light valve, andmeans associated with the light valvefor governing the light controlling characteristic thereof to compensatefor the distortion in a picture to be transmitted due to thenoncomplemental relationship of the corresponding tone values of thesubject and of the picture produced by an odd number of stages of thephotographic process.

2. In a picture transmission system, a picturereceiving mechanismincluding a ,light valve, and optical means associated with said valvefory governing the light controlling characteristic thereof to introduceinto the received picture a distortion which compenlationship of thecorresponding tone' values- Vby an odd number of stages of thephotosates for the. distortion in a. picture to be transmitted due tothe non-complementari reof the subject and of the picture producedgraphic process. j

3. In a picture transmission system, a pic- A ture receiving mechanismincluding a. light controlling device, and a. member associated withsaid device and having an aperture for introducing into the receivedpicture adis- .tortion'which compensates for the vphotographicdistortion in a picture to be transmitted due to the non-complementalrelationship of the corresponding tone values of the subject andofthepicture produced by an odd number of stages 'of the photographicprocess.

ture reproducing device inluding a l1 ht vave, and means associated withsaid va ve a picture transmission system, a pic-'- for governing thelight controlling characteristic thereof to ena le the reproduction of anegativefrom' a negative by compensating for the photographic distortionin. a picture to be transmitted due to thenon-complemental relationshipof the corresponding'tone` values of the subject and of the pictureproduced by Van odd number of stages of the photographic process.

5. The combination in a' system for the electrical transmission ofpictures, ofa picture reproducing device for enabling the directreproduction of negatives from negatives and positives from positivesincludinr optical means or compensating for the pthotoaphic distortionin a picture to be transmitted due to the non-complemental relationshipof the corresponding tone values of the subject and of the pictureproduced by an odd number of. stages of the photographic process. v

6. In a picture transmission system, la. light valve including anaperture the opening of which may be varied by a movable element, andoptical means associated with the light valve to compensate forphotographic distortion in a` picture to be transmitted due to thenon-complemented relationship of" the corresponding tone 'values'of thesubject and of the 'picture produced by an odd number of stages of thephotographic process, said to compensate for photographic distortion,-

said means comprismg an apertured screen, the contour of thesaid apertuebeing such that the aperture when opened by the light valve permitsthepassage of lightsubstantially proportional to the reciprocal of thecurrent passing through'the movable element of the lightvalve;

- `8.,]n a picture transmission system,`re-

Vceiving apparatus comprising alight source,

a light valve, a screen of varying Alight -transvmitting power, a lensfor forming an image of the light valve upon saidscreen, a receivingelement, a second screen, a second lens adjacent said first screen for.forming an image of the aperture in the second screen upon saidelement, the light transmitting power of said first screen whencooperating with said valve being such as to compensate for thephotographic distortion inherent in a sin- 'gle photographic operation..

a. picture transmission system, a receivmg device including alight valvehaving of the jaws of said valve,

jaws, means for producing a virtual image and optical means associatedwith the virtual image of the jaws of the light valve to compensate forphotographic distortion'.

10. In a picture transmission system, a reoeiving device including alight valve having an Iaperture which may be opened varyin amounts by amovable element, and optic means associated with-the light valve tocompensate Afor photographic distortion; said means comprising anapertured screen, the

contour of the said aperture bein such that the rate'of opening when thelig t valveis being opened is substantially the reciprocal'- 15

